Hey there, my name is Greta Shum, and I'm writing to you from a ship in the Southern Ocean! I'll tell you about my adventures aboard this research vessel as well as the science. Learn more about my project in particular, at soccom.princeton.edu.

Wednesday, January 11, 2017

Wait! First let’s talk about batteries and bladders!

I’ve gotten a few questions about how the floats work, and now’s as good a time as any to answer them!

How does the float control its depth in the water?

Inside the float, near the base, there’s a bladder containing oil—mineral oil to be exact. The bladder has a pump that can either inflate the bladder or deflate it. Since we can’t change the mass, all we can do is change the volume. When the float needs to descend, the oil is compressed, using the pump. That increases the density, and the float sinks. When the float needs to rise, the pump releases pressure, and the density decreases, allowing the float to rise. This of course all means that the float itself has to have a very specific mass.

How long does the float “live”?

Technically, a SOCCOM float has enough battery life to take 268 profiles in the Southern Ocean. If we take a profile every 10 days. That gives us over over 7 years of data! Battery life isn’t the only thing that matters though. During the winters, the float is especially strained. Even with sea ice avoidance software, ice can still damage the float in stormy waters. The SOCCOM scientists will estimate the life of a float to be between 5 and 6 years—weathering 4 or 5 winters before it becomes unreliable or the battery runs out.

What happens when the float runs out of power?

When the battery dies, the float sinks sinks to the ocean floor, but sometimes, it can get washed ashore if it’s close enough to land. That’s why it’s got a sticker with contact information on it:

If someone finds a float, he or she can contact the scientists, and SOCCOM will retrieve and potentially be able to reuse the parts or learn more from the how it fared in the water. It would be great to be able to retrieve all the floats once they’re running low on battery, but ship time in the Southern Ocean is expensive and hard to come by. It’s far more cost-effective to use any and all ship time to deploy more floats, especially because the pollution caused by these floats is far and away less than any other data-collection method. Just think about a ship trying to collect all the profiles that a float collects! Just the fuel cost alone would be far dirtier than a float doing the job.

What uses the energy?

The lithium-metal battery inside the float powers three things: the bladder pump, the iridium satellite communications, and the sensors. About one half of the energy goes toward the pump; one quarter goes toward communication, and one quarter for the sensors.

P.S. We're about to deploy Sundevil Lion, named by Sandia Prep School in Albuquerque, NM!